1. Field of the Invention
The present invention relates to an optical sensor which senses visible or infrared radiation and is used to control the operation of various devices or to measure the environment.
2. Description of the Prior Art
A conventional optical sensor of this kind has been described in Japanese Laid-Open Patent Publication No. 62-261025, which comprises, as shown in FIG. 14, a converging lens 1, a light detector 2, a transmitting window 3, and an optical sensor element 4. The converging lens 1 causes a light ray incident at right angles onto the light detector 2 to transmit therethrough without refraction and causes a light ray incident onto the light detector 2 at great angles of incidence to refract greatly, to thereby collect light rays from all directions onto the light detector 2.
In a constitution such as that mentioned above, most of the light rays incident at right angles onto the transmitting window 3 are detected. On the other hand, light rays incident in a horizontal direction onto the transmitting window 3 are refracted by the converging lens 1 and only a part of the light rays reaches the transmitting window 3. FIG. 15 shows the change in the amount of light detected with the angles of incidence at the time when the amount of the light to be radiated is maintained at a fixed level. Given that the amount of light to be detected on the optical axis of the converging lens (i.e., at the angles of incidence of zero degrees) is 100, when the angles of incidence are 90 degrees, that is, light rays are incident upon the converging lens 1 in the horizontal direction toward the transmitting window 3, the amount of light to be detected becomes zero. In this way, in the case that a conventional concave lens formed of a spherical surface is used as a converging lens, the amount of light to be detected is highly dependent upon the angles of incidence, which causes difficulties in accurate measurement of light amounts.